Strains on the inner and outer surfaces were measured with electric. Failure analysis of a steam turbine casing semantic scholar. In the low pressure section lp cracking can also occur at the inlet sections, inner casings, support struts, bolt holes and diaphragm fits. Determination of stress intensity factors in low pressure turbine. Numerical analysis of fatigue life improvement by optimizing the startup phase for a mw supercritical steam turbine inner casing weizhe wang.
Most turbine casing alloys can be welded using either of two distinct procedures. Damage informatics for steam turbine components global journals. The 158 mw steam turbine high pressure inner casing presented nozzle port bridge cracking and erosion. Steam turbine highpressure casing repaircase history. Cracking of high pressure, high temperature steam turbine inner and outer. The important components steam turbine casing is shells, shaftend packing head, flange, bolts, inlet section and a diffuser 5, 6. Steam turbine upgrades improve reliability power engineering. Cracks were analysed at the root of the third blade row of lowpressure steam turbine. In the case of unit 3, scc was identified in both lp turbine rotors.
Residual life assessment of steam turbine casing containing crack defect. Cracking of high pressure, high temperature steam turbine inner and outer casings can result as a unit accumulates operating hours and cycles. When the inlet temperature of the reheat section becomes higher than 593c, there is a risk of temper embrittlement in the inlet portion of the lowpressure turbine rotor after longterm operation. Completion of the 54 inchblade low pressure turbine. Typical low and intermediate pressure steam turbine issues. This complicated topic will be discussed in our next turbine generator tip in the series. Flexible operations steam turbine high temperature casing cracking. Form this we can observe that, to get more power output the steam exhaust pressure is kept very low and this achieved by casing design. A steam turbine casing is essentially a pressure vessel with its weight sul ported at each. For various crack lengths at lp steam turbine disc stress intensity factors are determined.
Examples of marginal distributions for hp high pressure inner casing cracking event. Because of the continual problems of dovetail cracking and inner casing erosion with the plants lp turbines and the need to increase unit performance and reliability, ppl susquehanna llc. This is part two of a three part turbine tip series, discussing the most common steam turbine casing problems. Cracking is typically due to low cycle fatigue or fatigue in combination with high temperature creep. Pdf the failure of the first stage blade in a steam turbine of 55 mw was investigated. The cracks were caused by low cycle fatigue lcf due to thermal stress during rapid starting and loading. An increasing number of lowpressure steam turbinesespecially at. Steam turbine casing a turbine casing cylinder is a high pressure vessel with its weight supported at each end on the horizontal centre line. Casing repair welding considerations power services group.
In addition to the lowpressure turbine rotor exposed to stress corrosion cracking, the inner casing, journal bearing, thrust bearing, jack shaft, gland, oil retaining. Finite element calculations show that in many cases, repairs can overcome. Cracks were found in the roots of steam turbine blades of the third blade row la2 of. Cracks on the roots of turbine blades of the lowpressure turbine. Lowpressure turbine an overview sciencedirect topics.
Lowpressure inner casings with modern features, including. Remaining life assessment of a high pressure turbine casing in creep and low cycle service regime article pdf available in thermal science 17suppl. Remaining life assessment of a high pressure turbine casing in creep and low cycle service regime. An increasing number of lowpressure steam turbinesespecially at supercritical fossil unitshave experienced stress corrosion cracking in the blade attachment region of their lowpressure rotors. Pdf crack of a first stage blade in a steam turbine researchgate. There are usually different types of casing like 1. General quantitative threshold values for corrosion in low pressure turbines 21. Low cycle fatigue life estimation of steam turbine casing. These two factors contribute to an increased potential for turbine casing problems in these units. Fatigue crack was initiated from the internal wall of the tierod hole where. Repairing lowpressure rotors with cracked blade attachments. The inner shroud is assembled with a clearance around the tenon, and the.
The use of longer steam turbine laststage blades lsbs reduces the number of low pressure casings and, thus, a turbines total installed cost. Actually, some turbine manufactures use slight rotor cooling at the inlet of the lowpressure turbine even for the 566cclass reheat temperature. Pdf remaining life assessment of a high pressure turbine. Fracture analysis of a low pressure steam turbine blade. In the case of purely low cycle fatigue driven by surface stresses.